Correct option(c) activated sludge treatment
Explanation
The word activated sludge system is derived from the practice of adding aerobic heterotrophic bacteria to the incoming sewage, from a previous batch. This sludge inoculum contains large numbers of metabolising bacteria, together with yeasts, molds, and Protozoa. An especially important ingredient of the sludge are species of. Zoogloea bacteria, which form flocculant masses (floc) in the aeration tanks.
The activity of these aerobic micro-organisms oxidises much of the effluent's organic matter into carbon dioxide and water. When the aeration phase is completed, the floc (secondary sludge) is allowed to settle to the bottom, just as the primary sludge settles in primary treatment.
